This results in a higher relative detection noise, which makes it difficult to benefit fully from the higher sensitivity, resulting Pazopanib buy in a reduced signal-to-noise ratio Inhibitors,Modulators,Libraries (S/N). The important parameter from an application point of view is not the sensitivity, but the S/N, so whether an evanescent wave or a free-space sensor is preferred depends on the type of analysis system.In our case, the sensor is designed for on-chip electrochromatography systems with microfabricated separation columns [7�C10]. The pillar array that constitutes such a separation column is also used as a resonator for on-column label-free detection, where integrated waveguides couple infrared light into/out of the detection site, Figure 1.

The advantage of this approach lies in the fact that the detection system imparts no changes to the fluidics, thereby reducing the distortion of the analyte bands in the chemical separation process, and hence achieving a high resolution in the chemical analysis.Figure 1.Schematic view of an on-column 1D photonic Inhibitors,Modulators,Libraries crystal refractive index chemical sensor. The detection region consists of a pillar array and integrated waveguides Inhibitors,Modulators,Libraries coupling infrared light through the resonator.The periodicity introduced by the 1D pillar array, in terms of refractive index, symmetry and geometry, gives rise to a band where photons of a particular wavelength range are forbidden to propagate, similarly to the case of electrons in atomic crystals. Typically, this forbidden band is called a photonic band gap and is the reason for the appearance of stop bands in the reflection or transmission spectra, Figure 1.

Photonic crystal sensors are typically fabricated by etching an array of submicron holes in a high refractive index material (e.g., silicon thin film) [11�C14]. This is not a viable approach in our case, for two reasons. First of all, using a hole array, transport of the fluids in the plane of the photonic crystal is not possible, hence Inhibitors,Modulators,Libraries the sensor cannot be integrated with planar microfluidics with channel dimension in the same range as the microoptical structures. Therefore, a pillar array is used instead. Secondly, silicon with layer thicknesses of several 100 nm is too electrically conductive, thereby not supporting electroosmotic pumping in the final devices due to bubble formation from electrolysis of the buffer solution.

However, Dacomitinib using a glass instead of a silicon resonator has the disadvantage that the refractive index contrast between the sensor and the analyte is much lower. This issue is addressed by depositing a thin layer of amorphous silicon around the glass pillars to increase the finesse of the resonator. Having selleckchem such a thin layer prevents bubble formation from electrolysis, because the conductance of the a-Si layer is much lower than the conductance of the buffer solution in the fluidic channel [15].